Alan Shearer insists he is only in charge of Newcastle until the end of the season but last week he gave a 3½-year contract to the club's most exciting young player, 18-year-old striker Nile Ranger. It hardly looks like the action of a man thinking exclusively of the short term.

Shearer has twice been to watch Ranger in the reserves and, having promoted him to the first-team squad, believes he has "a big role" to play in the efforts to avoid relegation. The "Macheda effect" – throwing in a raw, uninhibited talent – has not gone unnoticed on Tyneside.

Starting with Sunday's trip to Tottenham, Shearer has six games left to keep Newcastle in the Premier League and Ranger could well prove his secret weapon.

The England Under-19 striker has scored 22 goals in the academy and reserve teams this season and at 6ft 2in with pace to burn, he offers a promising future for a club that has had few causes for optimism this season. For Ranger, though, the praise of Shearer and the new contract represents a break with a troubled past.

Newcastle have proved Ranger's redemption. At the age of 15 he was sentenced to 11 weeks in a Young Offenders Institute for his part in a street robbery. "Coming up here has completely changed my life," he said.

"I grew up in north London, in Wood Green and I got into trouble. It all starts with just messing around with friends and jokes that go too far. I started running with a gang in the area. We were convicted of street robbery in Muswell Hill. There was a weapon but we didn't use it.

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"They were cracking down on street crime so I got sent down. I wasn't with a professional club at the time and I didn't really realise what I was risking.

"There were seven of us charged and four of us were convicted. Jail was pretty rough but it taught me a lot. The most important thing I learned is that I never want to go back."

When he was released, Ranger joined Southampton's prestigious academy – Theo Walcott's alma mater – and despite his promising development on the pitch, he kept getting into trouble. "My behaviour let me down at Southampton,"

Ranger explained. "I'd already had two written warnings about my behaviour – stupid things like going out or messing around in the lodge. Then I was caught at the end of the season with a load of first-team kit that I'd taken. I only wanted to give it to my friends. But I gave them no choice and they kicked me out."

This crisis proved decisive. Rather than sink back into the London streets, Ranger decided to save his future. With the steadfast support of his mother Karen and a change of agents, things began to look up.

Swindon took him on trial and offered him terms but he had come to the attention of Dennis Wise in the meantime and he signed for Newcastle last July. "I was absolutely buzzing," Ranger said. "The change of atmosphere did me loads of good. I went into digs up here and I was away from the old faces, the old problems."

Under the careful tutelage of Richard Money, Newcastle's academy director, Ranger was a revelation. The goals started flying in and he was being feted as an English Emmanuel Adebayor. He was rewarded for his great performances with the Jackie Milburn award, which goes to the club's most impressive youth player. Kevin Keegan and Joe Kinnear both had him in their first-team squad but it is the arrival of Shearer that has really excited Ranger.

The player wasn't even born when Shearer came to national attention for scoring a hat-trick on his debut as a 17-year-old but he remembers watching him on Match of the Day.

"He's come down to watch the reserve games and has given me encouragement. He's told me if I keep working hard I will get my chance. It's incredible to get advice from someone like him."

Whether Ranger gets to work with Shearer in the long term is another matter but one thing Ranger is adamant about is that, whoever is in charge, he is determined to show his gratitude to Newcastle.

"I have changed," he said. "I realise now what an amazing opportunity this club has given me. I don't even want to think what might have happened to me if I hadn't come to Newcastle. I'm just so grateful for that."